The leggy 20-year-old blonde grew up in the leafy country-club suburb of Franklin Lakes with her parents and two older brothers and has quite a track record herself — as a sophomore sprinter at the University of Southern California.

Two weeks ago, the lovebirds were spotted browsing at Michael’s Sporting Goods in her hometown.

“He was wearing a Jets sideline cap, and they were checking out the football equipment,” reported one observer, who said they were like any other couple, low-key. “They wound up not buying anything.”

In April, the drop-dead gorgeous couple hung out together at a Lakers basketball game.

Although the dark-haired hunk has been linked to model Hilary Rhoda, it was Mueller who was at the Sanchez family home in Mission Viejo, Calif., celebrating when the $60 million golden arm was picked by the Jets on draft day in April.

During the celebration, the 22-year-old gridiron great found a moment in a quiet corner to plant a kiss on her cheek, according to the Orange County Register.

Mueller, who is double-majoring in public relations and computer science, attended a tony all-girls Catholic school, Immaculate Heart Academy in Bergen County.

It was there that she honed her running skills in the 200 and 400 meters and received All-State, All-League and All-County honors as team captain.

She is still close to her high-school coach and mentor, Shemayne Williams. During a Jets game against the New England Patriots in the Meadowlands two weeks ago, Mueller, who was with her parents in the stands, phoned her beloved coach “just to say hi,” Williams recalled.

Williams said Mueller met Sanchez through a California cousin before they both went to USC.

“I have not met Mark, but Jen’s family is from California — she knew him through a cousin and a circle of friends,” Williams said. “They knew each other before college and had a friendship for a while. They dated in college, and it evolved [into] a relationship now.”

Sanchez, who graduated from USC last year, has quickly become one of the NFL’s hottest commodities — leading the Jets to a 3-0 record.

“[Mark] is focused on his football. Jen is focused on getting through USC and trying to make her mark in society,” Williams said. “He looks like a great football player. He treats her great.”

The 5-foot-9 bombshell has another passion, too: cooking.

“She’s very serious about culinary cuisine and is planning a trip to France next summer,” Williams said.